新澳门六合彩内幕信息

The Lightness of Water Vapor Adds Heft to Global Climate Models

Climate Models Without the Lightness of Water Vapor Risk Uncertainty in Cloud Simulations

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Clouds hover over San Francisco, with skyline peeking through
Clouds hover over San Francisco. Low clouds, like those often covering California's coast, are among the most important clouds for climate change and the planet's energy balance. (Getty Images)

Quick Summary

  • Study adds a missing piece to the climate science puzzle of simulating clouds.
  • Lightness of water vapor influences the amount of low clouds.
  • Some leading climate models don't include this effect.
  • Including vapor buoyancy into climate models helps improve climate forecasting.

Clouds are notoriously hard to pin down, especially in climate science. 

from the University of California, Davis, and published in the journal Nature Geoscience shows that air temperature and cloud cover are strongly influenced by the buoyancy effect of water vapor, an effect currently neglected in some leading global climate models.

Global climate models are the primary tools used to study Earth鈥檚 climate, predict its future changes and inform climate policymaking. However, climate models often differ on the precise degree of future warming, largely due to their representation of clouds. 

鈥淐limate models are the best tool we have to predict future climate change,鈥 said lead author Da Yang, an assistant professor of atmospheric science at 新澳门六合彩内幕信息 Davis and faculty scientist at Lawrence Berkeley National Lab. 鈥淚t鈥檚 important that we actively try to improve them.鈥

Aerial satellite image of clouds over california coast
Clouds form over the California coast in 2002. (NASA)

Cold air rises? 

While conventional wisdom has it that hot air rises, the reverse is true in the tropical atmosphere, the study notes. Previous research by Yang and his colleagues proposed that cold air rises in the tropics because humid air is lighter than dry air. This effect is known as vapor buoyancy, and it regulates the amount of low clouds over the subtropical ocean. 

鈥淰apor buoyancy influences the distribution of low clouds鈥攖he kind of clouds we have off the California coast, which contribute greatly to the global energy balance,鈥 said Yang. 鈥淭he biggest challenge in accurately predicting future climate change is clouds, so we have to get vapor buoyancy right.鈥

The biggest challenge in accurately predicting future climate change is clouds, so we have to get vapor buoyancy right. 鈥 Da Yang

The study reported that six of the 23 widely-used climate models analyzed do not yet include this effect because water vapor is a trace gas, so its buoyancy effect has been considered negligible. But the study shows the vapor buoyancy effect is more significant than previously realized. In climate models without vapor buoyancy, the low cloud cover can be off by about 50% in certain regions.  

How clouds affect climate change

Low clouds are among the most important clouds for climate change and the energy balance of the planet because they reflect so much sunlight. Fewer low clouds can result in more absorbed sunlight and a warmer planet. More low clouds can make for a cooler landscape. 

鈥淚n a warmer climate, the buoyancy effect of water vapor would be increasingly important due to more atmospheric water vapor,鈥 Yang said. 鈥淚t is worth spending more effort to understand how water vapor buoyancy regulates Earth鈥檚 climate.鈥

The study鈥檚 additional co-authors include 新澳门六合彩内幕信息 Davis graduate student Seth Seidel and Wenyu Zhou, a former member of Yang鈥檚 group, now at the Pacific Northwest National Laboratory. 

The study was funded by Packard Fellowship for Science and Engineering, National Science Foundation, Lawrence Berkeley National Laboratory, and the U.S. Department of Energy.
 

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Media Resources

  • Da Yang, 新澳门六合彩内幕信息 Davis Land, Air and Water Resources, dayang@ucdavis.edu
  • Kat Kerlin, 新澳门六合彩内幕信息 Davis News and Media Relations. 530-750-9195, kekerlin@ucdavis.edu 
     

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